This invention relates to recovery of hydrocarbons from tar sands, and more particularly to an improved process for treating a bitumen-containing froth obtained from a primary extraction step.
There have been many proposed processes for recovering hydrocarbons from tar sands. U.S. Pat. Nos. 3,547,803; 3,553,100; 4,035,282 and 4,098,674 are representative of this group of proposed processes. The prior art processes generally involve a primary extraction step wherein some combination of hot water, steam and caustic is mixed with the tar sand to produce a bitumen-containing froth.
The processes then require some method of separating the hydrocarbon material from the froth by settling, centrifugation or the like. U.S. Pat. Nos. 3,607,721 and 3,901,791 disclose processes for upgrading the froth.
U.S. Pat. No. 3,547,803, previously referred to, discloses adding a diluent to the tar sand before the primary extraction step, and suggests a desalting step to treat recycle diluent after the hydrocarbon products from the tar sands have been recovered.
Finally, there is a commercial tar sands plant operating in Canada which adds a naphtha diluent to the froth followed by centrifugation to remove solids and water from the diluted bitumen. This process requires a distillation step to recover the naphtha diluent.
There has been a continuing search for improved tar sands processes which are effective and energy efficient.